14 Control of the degrees of substitution (DS) of these derivatives over a wide range is an important subject, as the properties of the obtained derivatives, including solvent solubility, swelling ratio of the crosslinked gels, degree of crystallinity and heat stability, are dependent on their DS values. 19, 20, 21 Water-soluble ionic PRs obtained by introduction of ionic groups can be further crosslinked to form ionic ‘slide-ring gels’, which have freely mobile crosslinks equipped with ionic groups, and show interesting properties, including swelling ratios up to ca 1200-fold and good responsiveness to electric fields. 12, 13, 14, 15, 16, 17, 18 For example, the introduction of various functional groups on the PR resulted in solubility of the obtained derivatives in water and a wide variety of solvents, 12, 13, 14 in contrast to the limited solubility of the unmodified PR. 8, 9, 10, 11 More recently, much attention has been focused on the synthesis, characterization and use of various PR derivatives, in which different types of functional groups were incorporated onto CD moieties to obtain a wide range of properties. 5, 6, 7 A PR consisting of poly(ethylene glycol) (PEG) as an axis and α-cyclodextrins as ring components is one of the most examined and used types of supramolecules, and has been used to create new materials such as conceptual ‘slide-ring materials’, 1, 2, 3 promising medical devices 4 and textiles with improved properties. In the last decade, a novel research area of advanced supramolecular materials science has developed as a result of investigations of various supramolecules, especially polyrotaxanes (PRs) and their derivatives, 1, 2, 3, 4 and progress in understanding their fundamental properties. The PR–glycine conjugates with higher DS values were soluble in a wide range of organic solvents, and all of the deprotected derivatives were water soluble. The DS values of the deprotected derivatives determined by colloidal titration agreed well with those of the protected conjugates determined by 1H nuclear magnetic resonance, suggesting no removal of the pendant glycines during deprotection. Successful deprotection of Z groups was achieved only by treatment with a trifluoroacetic acid/thioanisole mixture, but was unsuccessful using conventional hydrogenation and treatment with a hydrobromic acid/acetic acid mixture. Subsequent deprotection yielded cationic PR derivatives with different DS values. Varying the stoichiometric ratios gave the broadest DS control. A wide range of DS values were achieved by varying the reaction conditions, including the stoichiometric ratios of protected glycines to hydroxyls, reaction temperatures and reaction times. ![]() Two types of polyrotaxane (PR)–glycine conjugates with different degrees of substitution (DS) were prepared by N, N′-carbonyldiimidazole-mediated esterification.
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